The invention relates to methods and apparatus for the production of colored knitted nets. More particularly, the invention relates to apparatus and methods for coloring individual ribbons of knitted nets.
Knitted nets are currently used for products including sacks for agricultural produce, bird protection nets, shading nets, insect protection nets and nets for wrapping round bales of hay. Such knitted nets are generally produced in a process which includes production of a primary film, slitting of the film into individual ribbons, and orientating the ribbons by an I.S.O. ribbon production machine, and knitting the individual ribbons into a knitted net and winding the knitted net onto a roll by a Raschel knitting machine. The primary film may be produced in various colors according the intended application of the knitted net.
During production, individual ribbons may tear after orientation and sometimes during printing. A detecting device is therefore provided and positioned to detect ribbon breakage and stop the machine at the earliest moment. It will be appreciated that early detection is important because Raschel knitting machines cannot rotate backwards, opposite to the direction of the knitting. Thus, if ribbon breakage detection and machine stoppage is too late, the resulting knitted net is defective and cannot be repaired due to the construction of the machine. After knitting, the netting is wound on a roll and, as previously mentioned, the netting rolls cannot be unrolled in order to fix any defects.
As illustrated in FIG. 1, when the ribbon production and knitting machine layouts are viewed from above, it may be observed that the ribbon production machine 4 is many times narrower than the knitting machine 8. This is because after slitting and orienting the oriented ribbons 6 are knitted on a Raschel machine on which the distance between the needles is approximately 1" (25.4 mm). For example, if a film is slit "T10" (meaning 10 ribbons per inch) and 210 ribbons are knitted, the necessary film width is about 533 mm and the knitted net width is about 5,308 mm.
Because the ribbon production machine and the knitting machine are made by different manufacturers, each machine is provided with its own independent ribbon breakage detection device. Both machines use a type of device called a "Lamela". A Lamela is a hollow piece of metal through which an individual ribbon passes. When a ribbon tears, the corresponding Lamela moves downward (due to its weight) and makes electrical contact between two bars thereby stopping the machine. On the ribbon production machine 4, the Lamelas 3 are located at the horizontal point from which the ribbons begin to spread on their way to the knitting machine 8.
It may be appreciated that having 210 Lamelas in a width of about 533 mm creates problems giving rise to poor performance. Additionally, an inherent disadvantage of the Lamela system is that the Lamelas can only be located where the ribbons pass horizontally. Accordingly, the Lamela detection system is provided at the horizontal end 7 of the ribbon production machine 4. Similarly, on the knitting machine 8, the Lamela detection system is located on the first horizontal area 5 after spreading of the ribbons coming from the ribbon production machine 4.
The location of the Lamelas on the knitting machine has both advantages and disadvantages. An advantage is that a distance of 25.4 mm between ribbons provides adequate space for hanging Lamelas. A disadvantage is that due to friction, sticking, electrostatic charges, and the like, the Lamelas often either do not have sufficiently rapid response time or do not make electrical contact.
Frequently, there is a desire for knitted net which includes a strip of a particular color that differs from the overall color of the net. This may be for providing a strip of a particular shade at the end or middle of the net to indicate the netting product as originating from a specific supplier. Different color markings for similar products may also be used either for marking the end of a roll or in conjunction with a photoelectric cell to count the number of cuts.
A common method of coloring knitted netting is to use bobbins of different colored ribbons. These bobbins of colored ribbons are conveniently placed at the knitting machine and the colored ribbons are threaded into the machine as replacements for the original ribbons. Usually these colored ribbons have some amount of orientation and the bobbins are, therefore, located after the orientation stage in the net production process. The original ribbons of the overall color which have been replaced are automatically wound onto rolls and then recycled.
In the Raschel method of knitting, two types of ribbons are employed; transverse ribbons and longitudinal ribbons. When there is a desire to change color in the netting in the longitudinal direction, ribbons may be replaced as described above. When there is a desire to change color in the transverse direction for some length, however, the above described method may not be used as the knitting of the longitudinal ribbons takes less than a second. Shutting down the knitting machine, changing the ribbons, and restarting the machine to run for a such a short period of time is extremely inefficient even if longer lengths are to be colored.
Accordingly, the existing coloring method is only useful when there is a need to color longitudinal ribbons. Additionally, multiple colored ribbons must be stocked, each having characteristics compatible with the final product. The existing coloring method also introduces technical complications in the net knitting procedure causing wastage of raw materials and increase in the cost of the final product.
Accordingly, there is a need in the art to provide an efficient method and apparatus for coloring knitted nets during production of the netting.